1f: Principles of Data Communications: Multiplexing Techniques

Frequency Division Multiplexing

Frequency Division Multiplexing (FDM) works by transmitting all of the signals along the same high speed link simultaneously with each signal set at a different frequency. For FDM to work properly frequency overlap must be avoided. Therefore, the link must have sufficient bandwidth to be able to carry the wide range of frequencies required. The demultiplexor at the receiving end works by dividing the signals by tuning into the appropriate frequency.

FDM operates in a similar way to radio broadcasting where a number of different stations will broadcast simultaneously but on different frequencies. Listeners can then "tune" their radio so that it captures the frequency or station they want.

FDM gives a total bandwidth greater than the combined bandwidth of the signals to be transmitted. In order to prevent signal overlap there are strips of frequency that separate the signals. These are called guard bands.